


The Perils of Hybrid Monsters

by ArgentDandelion



Category: Undertale (Video Game)
Genre: Analysis, Biology, F/F, F/M, Gen, Genetics, Hybrids, Light Angst, M/M, Meta, Science, Weird Biology
Language: English
Status: Completed
Published: 2019-04-09
Updated: 2019-04-16
Packaged: 2020-09-25 05:40:54
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 1,823
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20371597
Author URL: https://archiveofourown.org/users/ArgentDandelion/pseuds/ArgentDandelion
Summary: Covers the possible health problems of cross-breed monster hybrids.





	1. Health Problems (General)

No, think of the children!…your hybrid children, that is.  
Contains lovely ideas for angst.

Hybrid fanchildren are common in the _Undertale_ fandom. It is likely this is because the main characters of the game cover multiple “breeds” of monster, and there are in fact canon cross-breed couples (Undyne and Alphys, RG01 and RG02). Fanchildren are also a creative exercise where one combines the looks and personalities of the parents into a new, distinct character design.

In-universe, if hybridization is even possible, it’s likely common. However, hybridizing could cause problems.

Where potential mates of their own species are rare, animals might hybridize with closely related species. Furthermore, animals might make hybrids if they’re compatible species kept in the same enclosure (e.g., lions and tigers in zoos).  
In birds when one species parasitically lays its eggs in the nests of another species, the offspring might imprint after its host parents in looks or song, and so only be interested in birds that look or sound like its host parents.

All these things likely happened when monsters were sealed underground. While it’s unclear if different monster breeds interbred before the war, given monsterkind’s massive casualties it’s likely monsters’ options within their own breed were limited. (This would surely be especially true for monster breeds that were rare to begin with.)  
Staying underground, especially if they all stayed in just one city for a long time, would also work like captive conditions.   
Furthermore, the devastation might have meant a whole lot of orphans, which might have been raised by different breeds. Such orphans might, like the parasitic birds, prefer breeds like the ones they were raised by. It’s certainly clear monsters have variable preferences and can imitate other monsters (e.g., Papyrus catching a thrown stick in his mouth)/have variable behavior, after all.

* * *

# Biological Problems

For some breeds, even if hybridizing is possible it would likely cause health problems. This is especially obvious for fire monsters, such as offspring of the Sans X Grillby (“Sansby”) pairing. Though skeleton monsters are apparently[1](https://argentdandelion.tumblr.com/post/184069215159/possible-health-problems-of-hybrid-fanchildren#fn:1) insensitive to cold, it’s unclear whether they’re insensitive or immune to heat too. Fan works often assume Grillby’s fire is painfully hot, and becomes much hotter when angry. While (dry, human) bones can withstand greater temperatures than human flesh without (visible) damage, being on fire constantly might be a problem. Even if the hybrid children can withstand it, it’s possible (and more likely) that they might hurt themselves from the higher temperatures if they ever get angry.

Pain can make people easier to anger, so being burned by their own flames might cause a self-destructive feedback loop of pain and burning. If they can’t quickly heal burn markings from such events, they might become anxious about it, akin to obvious scars or burn wounds.

### Environmental Unsuitability

Environmental unsuitability is also a problem. While a hybrid’s parents might be well-suited to distinct environments, the hybrid may be unsuited for either or require unpredictable intermediate environments.

For example, the fish monster Undyne is vulnerable to heat stroke/dehydration when travelling through the dry, hot caverns of Hotland; Alphys is not. Evidently travelling through Hotland is enough of a danger to Undyne that Alphys installed a water cooler for her halfway to her lab, even though Alphys’ lab is only a few screens into Hotland. While Undyne says she dislikes “snow”, she’s evidently not in danger standing outside Papyrus’s house indefinitely. This might not be true for Alphys: while some fish can live in cold water, reptiles either die or hibernate in cold environments like Snowdin.

A hybrid child of the two might do well in an intermediate environment (e.g., hot but humid, like south Florida) or take after one or the other unpredictably.

Some assume Undyne can breathe underwater through gills; what if the child prefers most of their body to be dry but needs to keep their gills moist? What if the child prefers dry, but not hot, environments? With such a potential blend of preferred environments, they all might need custom rooms (e.g., humidifiers, pools) in one house.

Most dangerously, what if Undyne can breathe water through her skin, but a reptile-skinned but otherwise fishlike child cannot? One work, [Scramble Saga](http://ut-scramble-saga.tumblr.com/post/165336986019/awfully-friendly-skeleton-he-shimmers-with), suggests Undyne sleeps in a water-filled bathtub rather than a bed. If a helpless baby that can’t breathe underwater is put in a tub-crib, the baby might drown. The child might drown, too, if Undyne is playing boldly and aggressively in the water and mistakenly assumes the child can breathe underwater.

* * *

## Psychological Problems

### No Horns

  
(The picture is based on goat skulls; notice they don’t have horns. Picture modified from [here](http://argentdandelion.tumblr.com/post/181850133682/a-rainbow-of-bones-resource-on-skeleton-monster).)

In goats, horn buds don’t grow directly from the skull, but from a specialized patch of skin. Only later do they start to merge to the skull.

Assuming Boss Monsters’ horns grow like that of goats, a Boss Monster-skeleton hybrid might not have horns. (Many such fanchildren have no skin, after all.) While many monsters do not have horns, this might still make the fanchild self-conscious about not having horns. (Perhaps [similarly](http://argentdandelion.tumblr.com/post/183411570841/kris-could-grow-horns-really) to Kris of Deltarune, though Kris is a human.)

Draft 1, April 6, 2019

### The Problems of Papyrus x Mettaton

> “Us ghosts spend our whole lives looking for a proper vessel. Slowly, slowly, we grow closer to our new bodies… Until one day, we too may become corporeal beings. Beings able to laugh, love, and dance like any other…” - Mad Dummy

It is unclear whether ghosts’ desire for vessels (or “bodies”) is biologically or culturally driven. Either way, hypothetical fanchildren of Papyrus and Mettaton are likely to be dissatisfied with their bodies.

[LordLaharl’s Vassal](https://lordlaharlsvassal.tumblr.com/post/152035409798/does-papyrus-have-a-negative-body-image-muscle) made a convincing point that Papyrus may have body dysmorphia issues. The Wikipedia article on the subject suggests part of the variation in body dysmorphia issues in the population (or “heritability”) can be explained by genetics. If this is true, and also true for monsters, a Papyrus x Mettaton child could have twice the body issues of either parent.

It’s unclear whether the child would be born/the equivalent of born a ghost fused with a skeleton body, a ghost possessing but not fused with a skeleton body, or be born separately as a ghost body and a skeleton body. If the Papyton child has a handy skeleton body from birth/the equivalent of birth, the child might not develop ghostly psychological problems, as the child could do normal non-ghost things with it.

* * *

**Related Reading**

[Inter-Species Socialization](http://argentdandelion.tumblr.com/post/183899667671/undertale-inter-species-socialization)

[Do Monsters Have Instincts?](http://argentdandelion.tumblr.com/post/182042292213/do-monsters-have-instincts)

* * *

  1. Dialogue from Papyrus is contradictory; he explains how he can live in Snowdin’s cold environment saying “I have no skin” but complains about the Annoying Dog having cold feet. [↩︎](https://argentdandelion.tumblr.com/post/184069215159/possible-health-problems-of-hybrid-fanchildren#fnref:1)


	2. Boss Monster/Skeleton Health Problems

> “We call ‘em Boss Monsters. When they have an offspring, the SOUL power of the parents flows into the child… Causing the child to grow as the parents age.” -**Gerson**

This quirk of Boss Monster reproduction could cause problems. (As Sans x Toriel, or “Soriel”, is the most popular cross-breed Boss Monster ship, this explanation will focus on that) The kinds of problems depend on whether it’s the children or parents who control SOUL power flow.

**Passive Vessel**

The diagram represents the means of soul flow as threads (literal or figurative) going from the parents to the child.

If the hybrid child is a passive vessel for SOUL power flow, the hybrid child’s growth might be stunted compared to a pure Boss Monster, since it has only one Boss Monster parent giving it SOUL power.[1](https://argentdandelion.tumblr.com/post/184234927050/the-perils-of-a-boss-monster-skeleton-hybrid#fn:1)

However, it’s also possible its growth is partly based on skeleton “genes”, for lack of a better word. If the two breeds grow at the same rate, the effects would cancel each other out, and the growth rate would be normal.

Still, if the growth rate of each is different (i.e., if Boss Monsters take much longer to mature than skeletons) it would be hard for either to figure out when to expect developmental milestones. What if Asriel made his first magical bullet at sixteen, but Sans made his at four?

**Active Vessel**

(Diagram supposing the child doubles the drainage rate and connections with Toriel, while not draining Sans)

This is the most dangerous possibility, not to the child but to the parents. This supposes the flow of SOUL power is something like mammal pregnancy, where a complex chemical interchange keeps the interests of the mother and embryo in balance.

If unable to draw the usual amount of SOUL power from one parent, the hybrid’s body/SOUL might double the drainage rate on Toriel, making her age twice as fast. However, if a Boss Monster hybrid drains whoever registers as its parents, regardless of breed, Sans’ “SOUL power” might flow to it as well.

Assuming it’s like human pregnancy, Boss Monsters’ bodies might be adapted to withstand the draining of SOUL power. (whether by controlling drainage rate or just by having a lot of SOUL power to start with) If skeletons don’t reproduce the same way, though, Sans’ body would have no adaptations to the drain of SOUL power. If he is “the weakest enemy” (e.g., has a weak constitution and presumed low SOUL power) and the child’s draining is particularly aggressive, Sans might be rapidly drained and die.

Sans’ body probably couldn’t counteract this. Again assuming pregnancy parallels, his child’s skeleton genes probably couldn’t counteract it either. Ligers are so big because they have a lion for a father but a tiger for a mother. The lion father’s genes encourage embryo growth, while tigresses (unlike lionesses) have no means of suppressing embryo growth. Indeed, it’s possible the child might inherit all the aggressive draining genes but no “whoa there, that would kill your parent” suppressing genes.

**Why Sans Would be a Good Father**

That title was somewhat misleading: there’s no evidence Sans would be an especially responsible or attentive father. But he might be great for siring hybrid children. Again assuming soul power draining is like an embryo drawing nutrients from its mother, it might be good that Sans is the father.

In mammals, the father’s genes build the embryo’s side of the placenta, an organ the embryo uses to get nutrients. The father’s genes encourage the placenta to draw in as many nutrients as possible; the mother’s genes (in her body) act to weaken it.

If the child itself causes the flow of soul power, and the power-draining trait is influenced by imprinting like the placenta, then a hypothetical Boss Monster/skeleton hybrid with a skeleton father might have weaker soul power draining. Theoretically, Toriel, or the pair overall, wouldn’t experience the same strain as Asgore and a hypothetical female skeleton would.

* * *

  1. The Asriel in[ Soul Dichromatism](https://archiveofourown.org/works/6883084/chapters/15702928) is an example: after Toriel died, his growth/physical maturation became stunted. He looks much younger than he actually is. Boss Monsters, in this work, also age slower than other monsters: 40 for Boss Monsters is biologically equivalent to sixteen for most breeds. [↩︎](https://argentdandelion.tumblr.com/post/184234927050/the-perils-of-a-boss-monster-skeleton-hybrid#fnref:1)


End file.
